1. Prior Art
The following is a tabulation of some prior art that presently appears relevant:
U.S. PatentsPatent NumberIssue DateInventors3,397,497Aug. 20, 1968Edward Fletcher4,809,474Mar. 7, 1989Carl E. Ekberg, Jr
2. Nonpatent Literature Documents
Product Catalog: Vulcraft Cellular Deck With Composite Stud Tables.
Prior art references describe the use of cellular steel decking as a self-supporting and composite pre-fabricated floor system. U.S. Pat. No. 4,809,474 is referenced since it associates the concepts of pre-stressing and steel decking. It differs from this patent application in that in this patent application, the steel decking itself is prestressed without the presence of any concrete. U.S. Pat. No. 3,397,497 shows a similar looking concept in its figure #6, but no mention of cambering or prestressing is made in their patent. Similarly, Vulcraft carries a line of cellular steel decks which are not prestressed or cambered. They mainly work in a multiple span condition. The difference with this patent application is that given the custom fabrication approach to every project, the decking assemblies are designed as simply supported spans and a custom camber is designed for each different span and load condition. The following are the current disadvantages that said systems pose:
1. Early top flange compression buckling when loaded with concrete topping and worker live load.
2. High deflections during concrete pour stage.
3. A preference to use the system in a multi-span fashion to diminish the detrimental effects of the previous two points, resulting in the need for intermediate support members.
4. An inability to customize said system for use in a project where a specific camber and prestress in the system would substantially improve system deflection and resistance performance.
The following are the main performance categories improved by the subject system when compared with conventional cellular composite decking (no prestress or cambering). Two loading stages are discussed. During the construction stage, the loads are those of the self weight of the deck, the concrete topping and the live load of the workers. Resistance is provided solely by the steel module. During the composite stage, the hardened concrete topping acts in compression and the middle and bottom deckings act in tension under the full design load.
1. Gravity load carrying capacity—Higher during the final stage and significantly higher during the construction stage due to the pre-tension in the top decking (1) and pre-compression in the middle decking (2) having to be overcome before a zero stress condition is achieved.
2. Instantaneous deflection performance—Higher, due to cambering having to be overcome first.
3. Long term deflection—Improved, due to the fact that only the superimposed loads will produce sustained compression in the composite topping.
4. Span versus total floor thickness ratio—Improved due to the prestress and camber during construction and final stage.
5. Cost per square foot—Improved, longer spans allow the omission of intermediate support members such as walls, columns and joists which require more end connections and footings.
6. Self-supporting (not requiring any formwork) during construction—Improved due to the camber and prestress enabling longer spans.
7. Initial investment cost to become a fabricator of the system—Reduced, due to the system being composed with standardized and commercially available components such as the top, middle, bottom deckings and self drilling screws.